Conventionally, as a power plant of this kind, there has been known one disclosed e.g. in PTL 1. In this power plant, a differential gear unit including first to fourth rotary elements is formed by combining first and second planetary gear units of a so-called single pinion type with each other. The rotational speeds of the first to fourth rotary elements satisfy a collinear relationship in which the rotational speeds are aligned in a single straight line in a collinear chart, in the mentioned order. Specifically, the first planetary gear unit includes a first sun gear, first pinion gears, a first carrier, and a first ring gear, and the second planetary gear unit includes a second sun gear, second pinion gears, a second carrier, and a second ring gear. The first sun gear and the second carrier are connected to each other via a hollow cylindrical first rotating shaft, and the first carrier and the second sun gear are connected to each other via a solid second rotating shaft. Further, the second rotating shaft is rotatably disposed within the first rotating shalt.
In the differential gear unit constructed as above, the first ring gear corresponds to the first rotary element, the first carrier and the second sun gear connected to each other correspond to the second rotary element, the first sun gear and the second carrier connected to each other correspond to the third rotary element, and the second ring gear corresponds to the fourth rotary element. Further, this conventional power plant is installed on a four-wheel vehicle, with the first rotary element connected to a first rotating electric machine, the second rotary element connected to a left drive wheel, the third rotary element connected to a right drive wheel, and the fourth rotary element connected to a second rotating electric machine. In the power plant, by controlling the first and second rotating electric machines, torque distributed to the left and right drive wheels is controlled.
Further, as the conventional power plant of the above-described kind, there has been known one disclosed e.g. in PTL 2. This conventional power plant is formed by combining first to third planetary gear units of the single: pinion type with each other, and includes first to fifth rotary elements that can transmit motive power therebetween. These first to fifth rotary elements are configured such that the rotational speeds thereof satisfy a collinear relationship, and in a collinear chart representing the collinear relationship, the rotational speeds of the first to fifth rotary elements are aligned in a single straight line, in the mentioned order. Specifically, the first planetary gear unit includes a first sun gear, first pinion gears, a first carrier, and a first ring gear, and the second planetary gear unit includes a second sun gear, second pinion gears, a second carrier, and a second ring gear. The third planetary gear unit includes a third sun gear, third pinion gears, a third carrier, and a third ring gear. The first carrier and the third ring gear are connected to each other via a hollow cylindrical first connecting portion, and the first ring gear and the third carrier are connected to each other via a cylindrical second connecting portion. Further, the third carrier and the second ring gear are connected to each other via a hollow cylindrical third connecting portion, and the second carrier and the third sun gear are connected to each other via a solid rotating shaft. Thus, the first to fifth rotary elements are formed.
Further, the power plant disclosed in PTL 2 is installed on a four-wheel vehicle, with the first rotary element connected to a first rotating electric machine, the second rotary element connected to a left drive wheel, the third rotary element connected to an engine, the fourth rotary element connected to a right drive wheel, and the fifth rotary element connected to a second rotating electric machine. By controlling the first and second rotating electric machines, torque distributed to the left and right drive wheels is controlled.